Electrical impedance tomography (EIT) aims to estimate the electrical properties at the interior of an object from current-voltage
measurements on its boundary. In this paper, preconditioned reconstruction algorithm which improves the
property of iterative convergence has been proposed to solve the inverse problem of EIT. Experimental results indicate
that the algorithm is much more stable and efficient compared with normal iterative methods. At the same time, the
invertible preconditioners and prior information of human thorax have been discussed in this paper.